1. Field of the Invention
This invention relates to a method for molding wet-felted fibrous material, and to the molded product produced by this method. More particularly, this invention relates to a method of molding a textured pattern of high fidelity on a wet-felded, mineral fiber-containing mat while the mineral fibers are in a wet and highly entangled condition.
2. Description of the Prior Art
The practice of embossing textured patterns and designs on the surfaces of ceiling tiles, ceiling panels and other substrates is widespread and the art of imparting a decorative appearance to these products is greatly varied. One basic technique in common usage is to employ an embossing plate or roll which impresses the pattern into the surface of a dry substrate, thereby often causing the surface to become crushed. Other conventional methods employed, such as cutting, abrading, or routing out a portion of the surface of the substrate, also involve deformation of the substrate.
The usual prior art methods of pattern embossing therefore generally entail the deformation, by pressure or other means, of the substrate. In the process, the fibers of the substrate become fragmented. Also, the binder loses its cohesiveness due to the fragmentation resulting from the pressure of the embossing plate or roll. As a result, the substrate becomes weak and vulnerable to humidity and the force of gravity. This weakening can cause the substrate to have poor dimensional stability and to sag from the ceiling if it is a ceiling panel or tile.
The current commercial practice in producing textured patterns on mineral board by dry embossing is to emboss a pattern on the dried core to a depth of about 0.045 inch to 0.065 inch by wetting the dry core surface with water, and then embossing by means of a hot roll. Due to fracturing of the mineral fibers, a significant loss in core strength results. A costly backsizing then is required to restore board handleability and high humidity sag properties. However, in the case of "deeply" embossed patterns of 0.100 inch to 0.200 inch, the loss in strength is so large that even backsizing will not help.
Another disadvantage associated with the prior art methods involving cutting, routing, and abrading is that they produce dust, thus creating a health and explosion hazard to workers. Complicated and expensive dust collection systems are required to cope with these hazards.
It would be highly desirable if an improved method of molding a textured pattern on a substrate could be found which is relatively simple and yields a molded substrate having superior strength and a highly detailed pattern on its surface.